This invention relates to the art of testing of semiconductors in-circuit, particularly those semiconductors which are shunted by a low resistance.
Semiconductors are now widely used in a number of different technological industries. Semiconductors include diodes, transistors, triacs, diacs, thyristors, silicon controlled rectifiers, and others. A significant amount of research is currently being done on new applications of semiconductors, and hence, it is anticipated that the use of semiconductors will expand into new areas as well as increase significantly in those areas where they are already used.
One of the most significant operational advantages of semiconductors is their long-term reliability. However, this significant advantage is decreased somewhat because semiconductors are typically very difficult to test for faults or defects, especially in-circuit. Many devices, such as curve tracers, multimeters, and beta testers have been developed to test semiconductors, but typically these devices are only effective when the semiconductor to be tested is first removed from the circuit. Even under the best of circumstances, the removal of a semiconductor is difficult and time consuming, and at worse is impossible, due to the likelihood of damage to the semiconductor by the act of removing it from the circuit.
A further difficulty with such conventional devices is that they are not capable of testing the quality of the performance of the semiconductor, i.e. they do not recognize impaired performance, due to such causes as damage or age. Such testers typically can recognize a nonfunctional semiconductor junction but the junction which is impaired, even sufficiently to seriously affect the circuit in which the semiconductor is connected, frequently will test good on the tester.
There are some testers, however, such as the ones shown and described in U.S. Pat. Nos. 3,973,198 and 4,074,195, which are owned by the assignee of the present invention, which are in fact capable of testing the operating condition of a semiconductor in-circuit. Those particular test instruments have gained increasing acceptance in the industry, but are, however, of limited use when the semiconductor being tested is shunted by a very low resistance, i.e. below 20 ohms. Also, the device disclosed in German Pat. No. 23 45 469 to Knox may in certain applications be capable of testing a semiconductor junction in-circuit, but it is significantly more limited in operational capability than the testers disclosed in the '198 and '195 patents, supra. The Knox apparatus is also not able to test semiconductors shunted by low values of resistance.
Accordingly, it is a general object of the present invention to provide an apparatus for testing the operating quality of semiconductor junctions which overcomes one or more of the disadvantages of the prior art discussed above.
It is another object of the present invention to provide such an apparatus which provides an indication of the condition of the semiconductor junction in-circuit, even when the semiconductor junction is shunted by a low resistance.
It is a further object of the present invention to provide such an apparatus which may be used in testing a wide variety of semiconductors.
It is yet another object of the present invention to provide such an apparatus which provides a readily interpretable visual indication of the condition of the junction being tested.
It is a still further object of the present invention to provide such an apparatus which is capable of providing an accurate indication of the condition of an impaired junction.